It is conventional to mount a current carrying thermostatic disc in a housing so that it will snap between contacts engaged and contacts disengaged configurations in dependence upon the temperature of the disc. Electrical current passing through the disc generates heat thereby raising the temperature of the disc. Current levels above a selected level will raise the temperature of the disc to a preselected actuation level at which point the disc will snap to a contacts disengaged configuration thereby breaking the electrical circuit until the disc cools off to a lower, reset temperature at which point the disc will automatically snap back to a contacts engaged configuration re-energizing the electrical circuit.
It is also conventional to provide manually resettable circuit breakers by using a thermostatic having a wide temperature differential, that is, a disc having a relatively low reset temperature and provide some mechanism to apply a force to the disc to cause it to reset. A switch of this type is shown in U.S. Pat. No. 2,696,538 by way of example. Such switches work well, however, they require the use of a reset plate and associated parts for applying a relatively high force without interfering with the trip free operation of the switch. That is, it is a requirement of this type of switch that the contacts be allowed to move to a contacts disengaged position even when the reset mechanism is held in the actuated position. This results in relatively complex parts. Further, making wide temperature differential discs is more difficult than making automatic resettable discs having a narrower temperature differential.
Another circuit breaker in commercial use employs an automatically resettable disc along with an electrically insulative, spring loaded member which rotates upon opening of the contacts to be positioned between the contacts to thereby prevent reengagement of the contacts. The circuit breaker is manually reset by rotating a lever attached to the spring loaded member to move the member out of alignment with the contacts. This type of circuit breaker has the disadvantage that the plastic member which drags across the contacts tends to melt and/or deteriorate and contaminate the contacts during repeated cycling thereby adversely effecting proper operation. Another disadvantage is that the lever mechanism penetrates an environmental gasket placed over the circuit breaker housing thereby subjecting the device to leakage of water and the like, a serious disadvantage when the circuit breaker is used in marine applications and the like.